1. Field of the Invention
The present invention relates to a power supply circuit for a flash discharge tube used to make a flash discharge tube such as a xenon flash lamp emit light.
2. Related Background Art
A flash discharge tube represented by a xenon flash lamp is widely used as a light source for spectroscopic analysis, a light source for a flash lamp of a camera, a lamp for a high-speed shutter camera or the like because the spectral characteristics of the output light thereof are approximate to sunlight and it can provide stable flash light having a very short light-emission duration. Rare gas such as xenon or the like is filled in such a flash discharge tube. By applying high-voltage pulse current to a trigger electrode disposed in the discharge tube, electrical breakdown is partially induced to form a route through which current flows, and main discharging charges flow from a negative electrode to a positive electrode along this route, so that ionized rare gas induces arc luminescence and light is emitted to the outside. Here, large current is required to be instantaneously supplied for the main discharge, and thus there is normally adopted such a method that a required amount of electricity is charged in a capacitor for the main discharge in advance, and current is supplied from the main discharging capacitor at the light emission time.
Residual inductance occurs in the electrical circuit constructed by the power supply circuit and the flash discharge tube after light is emitted in the discharge tube. Since a large amount of current is supplied to the flash discharge tube as described above, high energy is accumulated in the residual inductance after the light emission of the flash discharge tube. In order to counter this, a surge current diode having a cathode connected to the positive electrode of the flash discharge tube and an anode connected to the negative electrode of the flash discharge tube is secured to the power supply circuit. The energy accumulated in the residual inductance in the power supply circuit is led as surge current to the circuit comprising the surge current diode and the flash discharge tube to drain the energy and suppress excessive accumulation of the energy.